1. Field of the Invention
Embodiments of the invention described herein pertain to the field of submersible pump assemblies. More particularly, but not by way of limitation, one or more embodiments of the invention enable an abrasive handling submersible pump assembly diffuser.
2. Description of the Related Art
Submersible pump assemblies are used to artificially lift fluid to the surface in deep wells such as oil, water or gas wells. A typical electric submersible pump (ESP) assembly consists of an electrical motor, seal section, pump intake and centrifugal pump, which are all connected together with shafts. In gassy wells, charge pumps or gas separators are sometimes included into the assembly to improve gas handling capability. The electrical motor supplies torque to the shafts, which provides power to the centrifugal pump. Centrifugal pumps impart energy to a fluid by accelerating the fluid through a rotating impeller paired with a stationary diffuser. Multiple stages of impeller and diffuser pairs may be used to further increase the pressure and lift fluid to the surface of a well. Each impeller rotates within the diffuser to which it is paired. The diffuser does not rotate, but is mounted co-axially with the impeller and nests on the diffuser of the previous stage. FIG. 1 illustrates conventional stacked impeller and diffuser stages.
One challenge to economic and efficient ESP operation is pumping solid-bearing fluid, which can quickly cause abrasive and erosive wear on pump assembly components. In one example, oil and gas which are pumped from deep wells (up to about 12,000 feet deep) often contain sand, dirt, iron sulfide (FeS) and other abrasive contaminants (collectively or individually “media”). Pumps for these purposes have tight clearances and high rotational speeds, and are therefore highly susceptible to abrasive and erosive wear. Pump diffusers in particular are highly susceptible to abrasives. As solid laden fluid rotates through the centrifugal pump, apparent centrifugal forces push media against the walls of the diffusers causing “swirling” against the walls and floor. The swirling erodes the diffusers causing premature failure.
The smooth areas of diffusers predominantly affected by swirling are on the inlet and discharge side of the diffuser in the cavities created between the impeller and diffuser. These conventional cavities are illustrated in FIG. 1, which show conventional cavities 100. In this example, when operating in media bearing fluid, media will erode the floor of the conventional diffuser bowl near the bowl outer wall, as well as the bowl outer wall itself. In some instances, media erodes through the diffuser walls entirely and proceeds to erode through the pump housing surrounding the pump assembly. A pump with eroded hole(s) in its housing will typically have significantly reduced or no fluid production capability, an increased risk of motor overheating due to reduced fluid in the flow path, and in extreme circumstances, may cause a parting pump.
Recently attempts have been made to combat abrasive wear to pump components by adding anti-swirl ribs, called “sand dams” to the bowl of the diffusers. Sand dams create a perpendicular raised feature extruding into a conventional cavity between the impeller and diffuser. Sand dams attempt to direct media in the well fluid away from the diffuser walls where it would otherwise cause damage. A conventional diffuser with conventional sand dams is illustrated in FIG. 2. As shown in FIG. 2, conventional diffuser 200 includes rectangular conventional sand dams 205 extruding perpendicularly into the conventional diffuser bowl. However, conventional sand dams do not adequately counteract swirling. Grooves 210 in conventional diffuser wall 215 form due to contact with abrasives despite the presence of conventional sand dam 205. In addition, edges of conventional sand dam 205 where the sand dams 205 meets the diffuser wall 215 will continue to erode until worn through entirely. FIG. 3 illustrates the way in which a conventional sand dam 205 may influence the flow of media in produced well fluid. As shown in FIG. 3, abrasives in the fluid continue to gravitate towards the diffuser wall and cause wear to the conventional sand dam as well as the diffuser wall and floor—as conventional sand dams may cause abrasives to bounce between the wall and the sand dam. Although a conventional sand dam may increase the operational life of a diffuser, documented run times of diffusers with conventional sand dams are still unacceptably short, since once a diffuser has eroded it must be replaced. Replacing a diffuser means removing the submersible pump assembly from the well, which is costly and time consuming.
It would be an advantage for diffusers operating in abrasive environments to have an increased lifespan without excessive erosion. Therefore, there is a need for an abrasive handling submersible pump assembly diffuser.